Method of high pressure treatment

ABSTRACT

In a high pressure processing method for removing an unnecessary substrate on the surface of the surface of a workpiece by bringing it into contact with supercritical carbon dioxide and additives in a high-pressure chamber, removing the unnecessary substance on the workpiece, first rinsing and second rinsing are performed under a substantially same pressure with continuous flowing of supercritical carbon dioxide.

TECHNICAL FIELD

[0001] The present invention relates to a method of efficientlycleaning, developing or drying a workpiece that has fine structure(micro-structured surface) on their surface of such as a semiconductorsubstrate (wafer), for instance, a method of removing unnecessarymaterials such as resist and so on stuck onto a surface of a substratein a semiconductor manufacturing process off the substrate and removingtherefrom.

BACKGROUND ART

[0002] In the field of semiconductor devices, formation of fine patternshas been rapidly developed. The size of wiring in a device wassubstantially 1 μm about 10 years ago, it is substantially 0.18 μm atthe present time, and furthermore, devices having a wiring size of 0.13μm have almost come into practical use. Further, researches anddevelopments to manufacture semiconductor devices having a wiring sizefrom 0.10 μm to 0.07 μm, or even of 0.05 μm have been started.

[0003] Furthermore, along with a higher speed of the semiconductordevice, introduction of new materials is vigorously in study. Forinstance, as insulator, low dielectric constant (low-k) materialsattract increasing attention, and the possibility that porous materialsof organic materials and organic/inorganic composite materials are usedfor low-k materials and how to reduce the dielectric constant arerecently actively studied. The development of such semiconductor devicescauses various problems that have not been problematic so far.

[0004] For instance, in a cleaning process that is an important processin the manufacturing process of the semiconductors, so far, as acleaning method of semiconductor wafers, a wet cleaning method in whicha semiconductor is cleansed with a solution in which necessary additivesare added to ultra pure water has been adopted. After the cleaning, itis general to rinse the wafer with ultra-pure water, followed byapplying spin dryer in which the wafer is rotated to spin off water. Asthe additives, amine-based compounds or fluorinated compounds have beenselected in accordance with applications.

[0005] However, with the miniaturization of semiconductor devices andthe application of new materials, there have been caused problems byusing the water-based cleaning method. One of them is in that since thewater-based cleaning agent cannot permeate into fine via holes of adiameter of substantially 0.1 μm, the cleaning cannot be thoroughlyperformed. Though difference in the extent of permeation depends on thediameter of via hole and material, it is considered that the more thevia hole is miniaturized, the more difficult the cleaning becomes owingto physical properties such as the interfacial tension and viscositythat liquid intrinsically has.

[0006] Furthermore, in the case of the porous new materials that have alot of holes further finer than via hole, there have been the otherproblem that it is difficult to remove the cleaning liquid inside of thefine hole even if the cleaning liquid has permiated into the fine hole.

[0007] When water remains on a surface of a semiconductor wafer, variouskinds of inconveniences are caused in later processes; accordingly,drying after the cleaning is important. In this connection, along withthe miniaturization of the devices, occurrence of traces calledwatermark that remains after water is dried is also problematic.Furthermore, consuming a lot of precious water resource in the cleaningprocess cannot be said appropriate from a viewpoint of protection of theenvironment.

[0008] Similar problems have occurred also in the development process ofthe semiconductor wafers. In the development process of thesemiconductor wafers, exposed resist material is developed with anaqueous solution of TMAH (tetramethyl ammonium hydroxide). Thedevelopment process is followed by rinsing with ultra pure water furtherfollowed by drying by means of spin-dry. Accordingly, there are similarproblems as in the cleaning process of the wafers. Furthermore, there isa problem that the projected portions of the pattern are destroyed bythe capillary force generated in a gas-liquid interface and so onbecause a fine resist pattern is not such tough.

[0009] In order to solve the problems, recently, supercritical fluid hasbeen studied to use for cleaning and as a rinse liquid. A supercriticalstate means a state above the critical temperature and critical pressureintrinsic to a substance; it is a fourth state of a substance that isneither solid, nor liquid, nor gas; in the supercritical liquid,particularly, intermediate properties of the liquid and the gas stronglyappear. For instance, the density of the supercritical fluid is close tothat of the liquid; however the viscosity and diffision coefficient areclose to that of the gas. Accordingly, the supercritical fluid has thedensity close to the liquid on one hand, and has movability andpenetrating ability close to that of the gas on the other hand.

[0010] Industrially, carbon dioxide is most frequently used as thesupercritical fluid; this is because its critical pressure is low suchas 7.3 MPa, its critical temperature is close to room temperature suchas 31 degree centigrade, and it is nonflammable, inexpensive andharmless. Supercritical carbon dioxide has many excellent properties asa fluid that can be used in place of water in the cleaning process ofthe semiconductor devices.

[0011] First, the supercritical carbon dioxide can easily penetrate intothe via holes and fine pores of the porous material and can be easilyremoved therefrom. Accordingly, the difficulty in the cleaningaccompanying the miniaturization of the device can be solved. In thenext place, the supercritical carbon dioxide, having the density closeto that of the liquid as mentioned above, can contain a large quantityof a additives and a co-solvent; in other words, it means that thesupercritical carbon dioxide has cleaning ability comparable to ordinaryliquids. Still furthermore, since there is no need of using water in thecleaning process, all of the aforementioned problems such as the problemof remaining water, the problem of the watermark in the cleaningprocess, the problem of pattern destruction due to the interfacialtension and the problem of environmental destruction can be overcome byuse of the supercritical carbon dioxide.

[0012] In this connection, the present invention intends to provide themost preferable method when substances to be processed such assemiconductor wafers are processed with supercritical carbon dioxide.

DISCLOSURE OF THE INVENTION

[0013] A method according to the present invention is a high-pressureprocessing method for removing an unnecessary substance on the surfaceof a workpiece by bringing the surface of the workpiece into contactwith supercritical carbon dioxide and additives in a high-pressureprocessing chamber, said method comprising the steps of:

[0014] sealing said high-pressure processing chamber after loading saidworkpiece in said high-pressure processing chamber;

[0015] pressurizing said high-pressure processing chamber withpressurized carbon dioxide supplied to said high-pressure processingchamber to a predetermined pressure and a predetermined temperaturehigher than the critical pressure and critical temperature thereofrespectively;

[0016] dissolving said additives and a co-solvent in supercriticalcarbon dioxide by mixing said additives and said co-solvent with saidsupercritical carbon dioxide in the upstream of said high-pressureprocessing chamber;

[0017] removing an unnecessary substance on said workpiece whilemaintaining the inside of said high-pressure processing chamber higherthan the critical pressure and critical temperature of carbon dioxide,by supplying continuously a predetermined amount of a mixture fluid ofsaid additives, said co-solvent and said supercritical carbon dioxide tosaid high-pressure processing and ejecting a substantially equal amountof the high-pressure fluid to the predetermined supply amount from saidhigh-pressure processing chamber;

[0018] obtaining a first rinse fluid in which said co-solvent isdissolved in said supercritical carbon dioxide, by stopping feed of saidadditives and mixing said co-solvent with said supercritical carbondioxide in the upstream of said high-pressure processing chamber;

[0019] performing a first rinsing process for replacing the mixturefluid of said additives, said co-solvent and said supercritical carbondioxide in said high-pressure processing chamber with said first rinsefluid while maintaining the inside of said high-pressure processingchamber higher than the critical pressure and critical temperature ofcarbon dioxide, by supplying continuously a predetermined amount of saidfirst rinse fluid to said high-pressure processing chamber and ejectinga substantially equal amount of the high-pressure fluid to thepredetermined supply amount from said high-pressure processing chamber;

[0020] performing a second rinsing process for replacing said firstrinse fluid in said high-pressure processing chamber with saidsupercritical carbon dioxide while maintaining the inside of saidhigh-pressure processing chamber higher than the critical pressure andcritical temperature of carbon dioxide, by stopping supply of saidco-solvent, supplying continuously only supercritical carbon dioxide bya predetermined amount to said high-pressure processing chamber andejecting a substantially equal amount of the high-pressure fluid to thepredetermined supply amount from the high-pressure processing chamber;

[0021] stopping feed of carbon dioxide to said high-temperatureprocessing chamber;

[0022] decompressing said high-pressure processing chamber toatmospheric pressure; and

[0023] unloading said workpiece from said high-pressure processingchamber.

[0024] According to the method, supercritical carbon dioxide iscontinuously supplied to the high-pressure processing chamber, and asupply amount and an exhaustion amount thereof are set substantiallyequal; accordingly, a pressure in the high-pressure processing chambercan be maintained constant. As a result, there is no loss in the time ofeach process of removing unnecessary materials and the first and secondrinse processes; that is, a whole process can be carried out in a shortperiod of time. Furthermore, the high-pressure processing can beperformed under stable and uniform conditions with excellentreproducibility.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is an explanatory diagram showing an example of ahigh-pressure equipment for carrying out an invention method.

[0026]FIG. 2 is a scanning electron micrograph of a surface of asemiconductor device before cleaning in an embodiment.

[0027]FIG. 3 is a scanning electron micrograph of a surface of asemiconductor device after cleaning in an embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

[0028] As a high-pressure processing in a high-pressure processingmethod according to the invention, a typical example can be a cleaningprocess in which from a workpiece thereto unnecessary materials sticksuch as semiconductor substrates thereto resist and residue stick after,for instance, the etching, the unnecessary materials are peeled off andremoved. Furthermore, without restricting to the cleaning, all processes(for instance, drying, development and so on) in which unnecessarymaterials are removed from on the workpiece with supercritical carbondioxide and additives can be included in the high-pressure processingmethod according to the invention.

[0029] In the following, the high-pressure processing method accordingto the invention will be explained with reference to the drawings. InFIG. 1, an example of a high-pressure processor for carrying out theinvention method is shown. Inside of a high-pressure vessel 1, ahigh-pressure processing chamber 2 is partitioned and therein aworkpiece 3 such as a wafer or the like is processed. On a wall surfaceof the high-pressure vessel 1, temperature control means 4 are disposedto control a temperature inside of the high-pressure processing chamber2. The high-pressure vessel 1 is constituted freely openable so that theworkpiece 3 may be put in and taken out.

[0030] A first stage according to the invention method includes, afterinserting the workpiece 3 into the high-pressure processing chamber 2,closing the high-pressure vessel 1, and hermetically sealing thehigh-pressure processing chamber 2. A high-pressure valve 5 is alsoclosed. The inside of the high-pressure processing chamber 2 ispreferably heated by use of temperature control means 4.

[0031] A second stage includes supplying pressurized carbon dioxide tothe high-pressure processing chamber 2, and pressurizing the carbondioxide in the high-pressure processing chamber 2 to a supercriticalstate of a predetermined temperature and predetermined pressure equal toor more than the critical temperature and critical pressure thereof.Carbon dioxide is reserved in a liquid carbon dioxide cylinder 6 andpressurized to a necessary pressure by a pressure pump 7. Pressurizedcarbon dioxide is heated, by means of a heater 8, to a predeterminedtemperature equal to or more than the critical temperature.High-pressure valves 9 and 10 are opened, and thereby pressurized andheated carbon dioxide is supplied to the high-pressure processingchamber 2. Supplying carbon dioxide to the high-pressure processingchamber 2, a pressure inside of the high-pressure processing chamber 2is raised; accordingly, the supply of carbon dioxide to thehigh-pressure processing chamber 2 is continued until a predeterminedprocessing pressure equal to or more than the critical pressure. Thehigh-pressure processing chamber 2 is maintained at a predeterminedtemperature by use of temperature control means 4 provided to thehigh-pressure vessel 1. As the temperature control means 4, variousknown means such as a heating wire or passing of a thermal catalyst canbe adopted.

[0032] Going through the second stage, supercritical carbon dioxide ofthe predetermined temperature and pressure is filled inside of thehigh-pressure processing chamber 2. The temperature and pressure at thistime, though appropriately varied according to the workpiece and kindsof the unnecessary materials to be removed, are preferably in the rangesof from 35 to 70 degree centigrade and from 10 to 20 MPa, respectively.

[0033] In a third stage, high-pressure processing such as cleaning andso on is performed. The third stage includes mixing and dissolving theadditives, the co-solvent and carbon dioxide; and processing such as thecleaning and the like. First, when the second stage has come tocompletion, the high-pressure valve 10 is closed, and the high-pressurevalves 5 and 13 are opened. Furthermore, from a additives and co-solventstorage tank 11 that reserves the additives and co-solvent, by use of apump 12, a mixture of the additives and co-solvent is allowed to mergeinto a carbon dioxide supply line (merging point 14). Subsequently, bygoing through mixing unit 15, the additives and co-solvent are dissolvedin carbon dioxide, and thereby a homogenous dissolution state can beobtained. This is the mixing and dissolving process. The mixture, ifnecessary, is heated again by a heater 16 and supplied to thehigh-pressure processing chamber 2. The heater 16 is used when owing tomixing of the additives and co-solvent, a temperature of carbon dioxideis lowered and thereby the supercritical state disappears.

[0034] Subsequently, the high-pressure processing such as cleaning andso on is carried out. When the mixture fluid of carbon dioxide,additives and co-solvent is supplied to the high-pressure processingchamber 2, the high-pressure valve 5 is controlled so that a pressure inthe high-pressure processing chamber 2 is a pressure same as that of thesecond stage. Specifically, the high-pressure fluid of an amountsubstantially same as that of the mixture fluid supplied into thehigh-pressure processing chamber 2 is extracted from the high-pressureprocessing chamber 2, and thereby a pressure in the high-pressureprocessing chamber 2 is maintained at a constant value.

[0035] As the third stage is continuously carried out, supercriticalcarbon dioxide therein the additives and the co-solvent arehomogemeously mixed and dissolved is supplied constantly in a cleanstate to the high-pressure processing chamber 2 and comes into contactwith a surface of the workpiece 3 such as wafers. Then, unnecessarymaterials are dissolved from a surface of the workpiece 3 into acleaning fluid and removed. The high-pressure fluid that is contaminatedby dissolving the unnecessary materials, without remaining in thehigh-pressure processing chamber 2, is exhausted from the high-pressureprocessing chamber 2. Accordingly, the third stage that performs thecleaning and so on can be carried out stably and in a short period oftime.

[0036] Here, as the additives, fluorides can be preferably used in orderto remove also polymer contaminants such as resist and etching polymerstuck to a semiconductor substrate. Fluorides very thinly dissolve asurface of the workpiece 3, and, owing to a lift off effect, unnecessarymaterials on a surface of the workpiece 3 are excellently removed.

[0037] As specific examples of the fluoride, ammonium fluoride (NH₄F),quaternary ammonium fluorides containing nitrogen atom and hydrogen atomsuch as tetramethylammonium fluoride, tetraethylammonium fluoride,tetrapropylammonium fluoride, tetrabutylammonium fluoride, and cholinefluoride [HOCH₂CH₂N(CH₃)₃]⁺F⁻ can be cited. The fluorides have excellentcleaning power. Depending on the kind of the workpiece, fluoridesfurther containing carbon atom (for instance, among the above citedcompounds, compounds other than ammonium fluoride) are more effective.Polyalcohols such as polypropylene glycol may be used as the additivestogether with the fluorides.

[0038] Depending on the kind of the workpiece and the kind of theunnecessary material, the kind of the additives may be altered;quaternary ammonium hydroxides such as TMAH (tetramethylammoniumhydroxide), alkylamines, alkanolamines, hydroxylamines (NH₂OH), xylenes,methylisobutyl ketones and fluorinated polymers may be used as theadditives.

[0039] The additives can be dissolved with difficulty in supercriticalcarbon dioxide; accordingly, by using in combination a co-solvent thatcan be a dissolution auxiliary, a homogeneous cleaning fluid (mixturefluid of the additives, the co-solvent and carbon dioxide) can beobtained. Although the co-solvents are not restricted to particular onesas far as the additives and supercritical carbon dioxide are madecompatible, aliphatic alcohols, in particular, aliphatic alcohols havingone to three carbons such as methanol, ethanol, isopropanol and so oncan be preferably cited. This is because that these substances dissolveeasily in supercritical carbon dioxide; accordingly, by controlling anaddition amount thereof, the cleaning power can be controlled. One kindor two or more kinds thereof may be mixed and used.

[0040] The additives and the co-solvent can be supplied through separatesupply lines to a carbon dioxide supply line; however, it is preferablethat the additives and the co-solvent are mixed in advance and suppliedto carbon dioxide. Furthermore, it is also preferable mode to disposemixing unit 15 between the merging point 14 and the high-pressureprocessing chamber 2, and thereby uniformly dissolving the mixture ofthe additives and the co-solvent and carbon dioxide. In the case wherethe additives or the co-solvent is not uniformly dissolved in carbondioxide, the additives and co-solvent are contained as fine droplets incarbon dioxide. When such droplets come into contact with a surface ofthe workpiece 3, there are concerns in that troubles such as theworkpiece 3 being locally destroyed and the processing such as thecleaning being nonuniformly applied might be caused. Accordingly, thesethree components are preferable to be mixed and dissolved homogenously.

[0041] As means 15 for mixing, means in which a pipeline agitatorcontrols flow directions of carbon dioxide, additives and co-solvent andmerges these, for instance, so-called static mixer can be convenientlyused; however, known agitators can be used.

[0042] In the third stage, when a total amount of the mixture fluid ofthe additives, co-solvent and carbon dioxide is set at 100 mass percent,a ratio of a total amount of the additives and co-solvent, that is, (theadditives+co-solvent)/(the additives+co-solvent+carbon dioxide), ispreferably in the range of from 0.1 to 10 mass percent. When the ratiois smaller than 0.1 percent by mass, in some cases, the cleaning effectcannot be exhibited; however, when the ratio exceeds 10 percent by mass,the mixture becomes, rather than a supercritical fluid, a fluid close toliquid in its properties and unfavorable deterioration of propertiessuch as excellent penetrating power that supercritical carbon dioxidehas occurs. The ratio of a total amount of the additives and co-solventis preferably 5 or less mass percent, and most preferably in the rangeof from 1 to 2 percent by mass. Furthermore, a ratio of an amount of theadditives to a total amount of the additives and co-solvent in themixture fluid that is set at 100 mass percent, that is,(additives)/(additives+co-solvent), is preferably in the range of from0.1 to 5 percent by mass, and most preferably in the range of from 1 to2 percent by mass.

[0043] As mentioned above, by making an amount of the additives is madesmaller relative to that of carbon dioxide and co-solvent, processingcost can be reduced consequently. Furthermore, since many additives arestrong basic or toxic compounds, the reduction of an amount ofexhaustion of the additives contributes to environment and safetyproblem, and shortens a processing period of time necessary for thesubsequent rinse processing.

[0044] From a mixture fluid of supercritical carbon dioxide, theadditives, the co-solvent and the unnecessary materials, by use of, forinstance, a gas-liquid separator or the like, carbon dioxide isvaporized and taken out as a gaseous component, and other components maybe separated as a liquid component (solid may be partially contained);furthermore, as needs arise, various kinds of post processingappropriate for the respective components may be applied.

[0045] A fourth stage includes the process of obtaining a first rinsefluid from the co-solvent and carbon dioxide and the process of a firstrinsing. After the high-pressure processing such as the cleaning in thethird stage has come to completion, the high-pressure valve 13 isclosed; the pump 12 is stopped; instead, the high-pressure valve 19 isopened; and thereby the co-solvent is guided by use of the pump 18 fromthe co-solvent tank 17 to the merging point 14 and merged to carbondioxide there. By use of the mixing unit 15 and the heater 16, a firstrinse fluid made of supercritical carbon dioxide and co-solvent isobtained.

[0046] While supplying the first rinse fluid, similarly to the thirdstage by controlling the high-pressure valve 5, to the high-pressureprocessing chamber 2, a high-pressure fluid in the high-pressureprocessing chamber 2 is continuously exhausted by an amountsubstantially same as the supply amount. The first rinse processingtakes normally 0.5 to 2 minutes.

[0047] According to the fourth stage, clean supercritical carbon dioxidetherein the co-solvent is dissolved flows continuously through theinside of the high-pressure processing chamber 2, and, while rinsing asurface of the workpiece 3, removes the contaminated high-pressure fluidgenerated in the third stage to the outside of the high-pressureprocessing chamber 2. The unnecessary (contaminated) substances and theadditives that are normally low in the solubility into supercriticalcarbon dioxide are dissolved in carbon dioxide by the help of theco-solvent. Accordingly, when only supercritical carbon dioxide isflowed in the first rinsing process, there is concern in that theunnecessary substances and the additives precipitate and stick again toa surface of the workpiece 3. Accordingly, it is necessary that, afterthe processing such as the cleaning is carried out, the first rinsefluid in which the co-solvent is dissolved in supercritical carbondioxide, that is, the first rinse fluid that can dissolve theunnecessary substances and the additives is flowed, and thereby theunnecessary substances and the additives are removed from thehigh-pressure processing chamber 2.

[0048] In a subsequent fifth stage, the second rinsing is carried out.The second rinse fluid is made of supercritical carbon dioxide alone.When the supercritical carbon dioxide is flowed through thehigh-pressure processing chamber 2, the co-solvent remaining in thehigh-pressure processing chamber 2 is completely removed, and therebythe cleaning and rinsing of the workpiece 3 come to completion.

[0049] Specifically, after the completion of the first rinsing in thefourth stage, the high-pressure valve 19 is closed, the pump 18 isstopped, the high-pressure valve 10 is opened, and carbon dioxide, underpressure by means of a pump 7, is heated with a heater 8 and supplied tothe high-pressure processing chamber 2. Similarly to the above third andfourth stages, the high-pressure valve 5 is controlled so that thesupply amount and the exhaust amount may become same, and thereby aninternal pressure of the high-pressure processing chamber 2 is keptconstant. The second rinsing normally takes substantially 0.5 to 2minutes.

[0050] A sixth stage is depressurizing. The pump 7 is stopped, whilestopping the supply of carbon dioxide to the high-pressure processingchamber 2, carbon dioxide inside of the high-pressure processing chamber2 is exhausted through the high-pressure valve 5, and thereby a pressureinside of the high-pressure processing chamber 2 returns to atmosphericpressure. Also in the depressurizing, a temperature in the high-pressureprocessing chamber 2 is preferably maintained at a predeterminedtemperature by use of temperature control means 4. When thehigh-pressure processing chamber 2 is heated, carbon dioxide remainingtherein, with a decrease in the pressure, changes from the supercriticalstate without going through a liquid state to a gaseous state andvaporizes; accordingly, the trouble that is caused during the dryingwhen water is used as a base of cleaning liquid is not at all caused;that is, stain or the like is not generated on a surface of theworkpiece 3, and furthermore, fine patterns are not destroyed.

[0051] Before applying the sixth stage, as needs arise, the thirdthrough fifth stages may be repeated, and thereafter the sixth stage maybe performed. It is because when each of the periods of time of thethird through fifth stages is shortened and repeated, a whole processingtime can be shortened in some cases. It can be appropriately selectedaccording to shapes or situations of the workpiece 3.

[0052] In a final seventh stage, the tightly sealed high-pressure vessel1 is opened, and the workpiece 3 is taken out. Thereby, all stages andall processing come to completion.

[0053] In the above, the high-pressure processing method according tothe invention has been explained with reference to FIG. 1; however,adding means known to industry segments and changing and applying theinvention in the range that does not deviate from the scope of theinvention are all included in the invention.

[0054] In the following, the invention will be detailed with anembodiment; however, the invention is not restricted to the followingembodiment.

[0055] Embodiment

[0056] With a high-pressure equipment shown in FIG. 1, the inside of ahigh-pressure processing chamber 2 was heated to 40 degree centigrade byuse of temperature control means 4 (heater). A high-pressure vessel 1was opened, a semiconductor wafer 3 was loaded, the high-pressure vessel1 was hermetically sealed, and an internal temperature of thehigh-pressure processing chamber 2 and a temperature of thesemiconductor wafer 3 were kept at 40 degree centigrade. After ahigh-pressure valve 5 was set so as to maintain a pressure at 15 MPa,high-pressure valves 9 and 10 were opened, and liquid carbon dioxide wasintroduced from a liquid carbon dioxide cylinder 6 to the high-pressureprocessing chamber 2 until a pressure same as that of the cylinder wasattained. Then, a pressure pump 7 was operated, and carbon dioxide wasintroduced at a flow rate of 10 g/min until a pressure inside of thehigh-pressure processing chamber 2 became 15 MPa.

[0057] In the next place, the high-pressure valve 9 was closed; ahigh-pressure valve 13 was opened; and, from a storage tank 11 of amixture of additives and co-solvent, with a pump 12, the additives andco-solvent were allowed to merge into carbon dioxide. In the storagetank 11, a mixture containing in a ratio of 0.1 mass percent of ammoniumfluoride and 0.9 mass percent of polypropylene glycol as additives and99 mass percent of ethanol as a co-solvent was reserved. A flow rate ofthe mixture was set at 0.4 g/min. Accordingly, a ratio of a total amountof the additives and the co-solvent in a cleaning fluid (additives andco-solvent and carbon dioxide) supplied into the high-pressureprocessing chamber 2 was 3.8 percent.

[0058] One minute after the additives and the co-solvent were supplied,the high-pressure valve 13 was closed; the pump 0.12 was stopped;instead, the high-pressure valve 19 was opened; a pump 18 was operated;thereby ethanol from an ethanol storage tank 17 was allowed to mergeinto carbon dioxide; and thereby the first rinsing was carried out.

[0059] One minute after the start of ethanol supply, the high-pressurevalve 19 was closed, and the pump 18 was stopped.

[0060] Furthermore, the high-pressure valve 10 was opened, thesemiconductor wafer 3 was rinsed with carbon dioxide alone, and therebythe second rinsing was carried out. After one minute, the high-pressurevalve 9 was dosed and the pump 6 was stopped. A pressure setting of thehigh-pressure valve 5 was controlled, and thereby the high-pressureprocessing chamber 2 was gradually depressurized to atmosphericpressure. Finally, the high-pressure vessel 1 was opened, and thesemiconductor wafer 3 was taken out.

[0061] Scanning electron micrographs of the semiconductor wafer 3 beforeand after the cleaning are shown in FIGS. 2 and 3, respectively. It canbe seen that fine stains in the surroundings of the via holes wereremoved owing to the cleaning.

INDUSTRIAL APPLICABILITY

[0062] In the high-pressure processing according to the invention, thehigh-pressure processing such as the cleaning and the first and secondrinsing are performed under the same pressure; accordingly, there is noloss time between the respective processes, resulting in performing thewhole process in a short period of time. Furthermore, the high-pressureprocessing can be performed stably, uniformly and with reproducibility.Accordingly, the present invention method can be preferably applied as acleaning method of semiconductor substrates with the supercriticalcarbon dioxide, or as development and drying methods.

1. A high-pressure processing method for removing an unnecessarysubstance on the surface of a workpiece by bringing the surface of theworkpiece into contact with supercritical carbon dioxide and additivesin a high-pressure processing chamber, said method comprising the stepsof: sealing said high-pressure processing chamber after loading saidworkpiece in said high-pressure processing chamber; pressurizing saidhigh-pressure processing chamber with pressurized carbon dioxidesupplied to said high-pressure processing chamber to a predeterminedpressure and a predetermined temperature higher than the criticalpressure and critical temperature thereof respectively; dissolving saidadditives and a co-solvent in supercritical carbon dioxide by mixingsaid additives and said co-solvent with said supercritical carbondioxide in the upstream of said high-pressure processing chamber;removing an unnecessary substance on said workpiece while maintainingthe inside of said high-pressure processing chamber higher than thecritical pressure and critical temperature of carbon dioxide, bysupplying continuously a predetermined amount of a mixture fluid of saidadditives, said co-solvent and said supercritical carbon dioxide to saidhigh-pressure processing and ejecting a substantially equal amount ofthe high-pressure fluid to the predetermined supply amount from saidhigh-pressure processing chamber; obtaining a first rinse fluid in whichsaid co-solvent is dissolved in said supercritical carbon dioxide, bystopping feed of said additives and mixing said co-solvent with saidsupercritical carbon dioxide in the upstream of said high-pressureprocessing chamber; performing a first rinsing process for replacing themixture fluid of said additives, said co-solvent and said supercriticalcarbon dioxide in said high-pressure processing chamber with said firstrinse fluid while maintaining the inside of said high-pressureprocessing chamber higher than the critical pressure and criticaltemperature of carbon dioxide, by supplying continuously a predeterminedamount of said first rinse fluid to said high-pressure processingchamber and ejecting a substantially equal amount of the high-pressurefluid to the predetermined supply amount from said high-pressureprocessing chamber; performing a second rinsing process for replacingsaid first rinse fluid in said high-pressure processing chamber withsaid supercritical carbon dioxide while maintaining the inside of saidhigh-pressure processing chamber higher than the critical pressure andcritical temperature of carbon dioxide, by stopping supply of saidco-solvent, supplying continuously only supercritical carbon dioxide bya predetermined amount to said high-pressure processing chamber andejecting a substantially equal amount of the high-pressure fluid to thepredetermined supply amount from the high-pressure processing chamber;stopping feed of carbon dioxide to said high-temperature processingchamber; decompressing said high-pressure processing chamber toatmospheric pressure; and unloading said workpiece from saidhigh-pressure processing chamber.
 2. The high-pressure processing methodas set forth in claim 1, wherein said co-solvent is an aliphaticalcohol.
 3. The high-pressure processing method as set forth in claim 2,wherein, said co-solvent comprises at least one alcohol selected from agroup consisting of aliphatic alcohols having 1 to 3 carbons.
 4. Thehigh-pressure processing method as set forth in claim 1, wherein saidadditives contain a fluoride.
 5. The high-pressure processing method asset forth in claim 4, wherein said fluoride is a compound that containsa nitrogen atom and a hydrogen atom.
 6. The high-pressure processingmethod as set forth in claim 1, wherein a ratio of a total amount ofsaid additives and said co-solvent is between 0.1 and 10 mass percent,to the combination of said additives, said co-solvent and saidsupercritical carbon dioxide.
 7. The high-pressure processing method asset forth in claim 1, wherein in the mixture fluid of said additives andsaid co-solvent is between 0.1 and 5 mass percent, to the combination ofsaid additives, said co-solvent and said supercritical carbon dioxide.8. A high-pressure processing method as set forth in claim 1, furtherincluding the step of, supplying the combination of said additives, saidco-solvent and said carbon dioxide, or the combination of saidco-solvent and said carbon dioxide to said high pressure chamber, aftermixing the combination mechanically.
 9. A high-pressure processingmethod as set forth in claim 1, further including the step of, supplyingthe combination of said additives, said co-solvent and said carbondioxide, or the combination of said co-solvent and said carbon dioxideto said high pressure chamber, after mixing the combination andreheating.